Why is the dribbling icing inside of Donut instead of being on the top?
Seeing how you've enabled face snapping, the issue is with how you've extruded the edge. If you took a cross-section of the donut shown below, your icing is cutting into the donut, represented by the highlighted line. Since you've also got a very thin solidify modifier, the icing isn't thick enough to push outside of the donut.



Rather than just extruding once, consider splitting it into multiple segments, so it follows the surface of the donut more closely. Notice how parts of the icing wireframe end up going beneath the donut mesh, but its close enough so that the solidify modifier (which was hidden so you could see the wireframe) could push the icing above the donut's surface.